Open Domain Event Extraction from Twitter

Alan RitterMausam, Oren Etzioni, Sam Clark

University of Washington

Goal: Realtime Stream of Structured Information About Events

iPadTYPE:

LaunchDATE:Mar 7

Steve JobsTYPE:DeathDATE:Oct 6

YelpTYPE:IPO

DATE:March 2

TIME

Q: which set of events do we want to know about?

Q: How soon can we know about an event?

Q: Where might we find information about events unfolding in the world?

• Structured / Semi-Structured data sources?– Facebook / Eventbrite– HTML / Wrapper induction

• Natural Language / Text?– News articles– Status Messages / Twitter

Claim: This is worth

investigating

Calendar Demo

http://statuscalendar.com

• Extract Named Entities– 1% sample of global Twitter stream– 2.5 Million / Day– Using NER trained on Labeled Tweets

• [Ritter et. al. EMNLP 2011]

• Extract and Resolve Temporal Expressions– For example “Next Friday” = 09-09-11

• Count Entity/Day co-occurrences– G2 Log Likelihood Ratio

• Plot Top K Entities for Each Day

Background: Event Extraction from Newswire

• Historically, the most important source of info on current events– Since spread of printing press

• Lots of previous work on Newswire– Timebank– MUC & ACE competitions• Limited to narrow domains• Performance is still not great

Social Media

• Competing source of info on current events• Status Messages– Short– Easy to write (even on mobile devices)– Instantly and widely disseminated

• Double Edged Sword– Many irrelevant messages– Many redundant messages

Information Overload

Noisy Text: Challenges

• Lexical Variation (misspellings, abbreviations)– `2m', `2ma', `2mar', `2mara', `2maro', `2marrow', `2mor', `2mora', `2moro', `2morow',

`2morr', `2morro', `2morrow', `2moz', `2mr', `2mro', `2mrrw', `2mrw', `2mw', `tmmrw', `tmo', `tmoro', `tmorrow', `tmoz', `tmr', `tmro', `tmrow', `tmrrow', `tmrrw', `tmrw', `tmrww', `tmw', `tomaro', `tomarow', `tomarro', `tomarrow', `tomm', `tommarow', `tommarrow', `tommoro', `tommorow', `tommorrow', `tommorw', `tommrow', `tomo', `tomolo', `tomoro', `tomorow', `tomorro', `tomorrw', `tomoz', `tomrw', `tomz‘

• Unreliable Capitalization– “The Hobbit has FINALLY started filming! I cannot wait!”

• Unique Grammar– “watchng american dad.”

Off The Shelf NLP Tools Fail

Off The Shelf NLP Tools Fail

Twitter Has Noisy & Unique Style

Annotating Named Entities

• Annotated 2400 tweets (about 34K tokens)• Train on in-domain data

Learning

• Sequence Labeling Task• IOB encoding

• Conditional Random Fields • Features:– Orthographic– Dictionaries– Contextual

Word Label T-Mobile B-ENTITY

to O

release O

Dell B-ENTITY

Streak I-ENTITY

7 I-ENTITY

on O

Feb O

2nd O

Performance (NE Segmentation)

Stanford T-NER0

0.1

0.2

0.3

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0.6

0.7

0.8

PRF

Event-Referring Phrases

Examples:Apple to Announce iPhone 5 on October 4th! YES!iPhone 5 announcement coming Oct 4th

WOOOHOO NEW IPHONE TODAY! CAN’T WAIT!

• Useful to display in connection with events– E.g. “Steve Jobs” + “died” + “October 6”

• Helpful in categorizing Events into Types

Event Phrases:Annotation/Learning

• Annotated 1,000 tweets (19,484 tokens)• Similar to EVENT tags in TimeBank• Sequence-labeling problem– IOB Encoding– Conditional Random Fields

Event Segmentation Results

Event Representation

Categorizing Event Types• Would like to categorize events into types, for

example:– Sports– Politics– Product releases– …

• Benefits:– Allow more customized calendars– Could be useful in upstream tasks

Classifying Events:Challenges

• Many Different Types• Not sure what is the right set of types• Set of types might change– Might start talking about different things– Might want to focus on different groups of users

Solution: Unsupervised Event Type Induction

• Latent Variable Models– Generative Probabilistic Models

• Advantages:– Discovers types which match the data– No need to annotate individual events– Don’t need to commit to a specific set of types– Modular, can integrate into various applications

Each Event Phrase is modeled as a mixture of types

Each Event phrase is modeled as a mixture of types

Each Event Type is Associated with a Distribution over

Entities and Dates

P(SPORTS|cheered)= 0.6P(POLITICS|cheered)= 0.4

Details…

• Gathered about 65M (entity, event, date) tuples

• Collapsed Gibbs Sampling– 1,000 iterations of burn in– Parallelized sampling (approximation) using MPI

[Newman et. al. 2009]

• 100 Event Types

Experiment: Categorizing Events

• Randomly Sampled 500 (entity, date) pairs• Annotated with event types– Using types discovered by the topic model

• Baseline:– Supervised classification using 10-fold cross

validation– Treat event phrases like bag of words

Event Classification Performance

End-to-end Evaluation

• Evaluate end-to-end calendar entries• Collect tweets up to cutoff date• Extract Named Entities, Event Phrases, Temporal

Expressions• Classify Event Type• Rank Events• Pick top K events occurring in a 2 week future

window• Evaluate Precision

• Ngram Baseline– No Named Entity Recognition– Rely on significance test to rank ngrams– A few extra heuristics (filter out temporal

expressions etc…)

End-to-end Evaluation

Shallow Syntax in Tweets: Difficult

• Performance Lower than News:– Entity Segmentation– Event Phrase Segmentation

• But:– Tweets are self contained– Short (usually not very complicated)– Simple discourse structure– Meant to be understood in isolation– More data

Contributions

• Analysis of challenges in noisy text• Adapted NLP tools to Twitter http://github.com/aritter/twitter_nlp• Calendar Demo

http://statuscalendar.com• Unsupervised Event Categorization– Discovers types which match the data

THANKS!